Back to EveryPatent.com
| United States Patent |
5,180,759
|
|
Neu
, et al.
|
*
January 19, 1993
|
Exothermic compositions
Abstract
An exothermic composition comprises a particulate readily oxidizable metal
such as aluminum, magnesium or silicon and an organic fluorine-containing
compound, and usually an oxidizing agent for the readily oxidizable metal.
The preferred organic fluorine-containing compound is
polytetrafluoroethylene. The composition may also contain a binder, a
particulate refractory material, refractory fibres and/or organic fibres.
The composition may be used in the casting of molten metal, either in
particulate form or as a preformed shape such as a sleeve or board, to
cover or surround molten metal in the feeder of a casting mould or in the
head or head box of an ingot mould.
| Inventors:
|
Neu; Max G. (Lichfield, GB);
Gough; Michael J. (Gnosall, GB)
|
| Assignee:
|
Foseco International Limited (Birmingham, GB2)
|
| [*] Notice: |
The portion of the term of this patent subsequent to August 30, 2005
has been disclaimed. |
| Appl. No.:
|
185997 |
| Filed:
|
April 25, 1988 |
Foreign Application Priority Data
| Current U.S. Class: |
523/141; 523/143; 524/430; 524/433 |
| Intern'l Class: |
C21D 007/00; C21D 003/18 |
| Field of Search: |
523/141,143,430,433
|
References Cited
U.S. Patent Documents
| 3635877 | Jan., 1972 | Van Wyk | 523/145.
|
| 4031046 | Jun., 1977 | Tisza | 523/141.
|
| Foreign Patent Documents |
| 681547 | Mar., 1964 | CA | 524/546.
|
| 627678 | Oct., 1949 | GB.
| |
Primary Examiner: Schofer; Joseph L.
Assistant Examiner: Mulcahy; Peter D.
Attorney, Agent or Firm: Nixon & Vanderhye
Parent Case Text
This is a division of application Ser. No. 035,458, filed Apr. 7, 1987.
Claims
We claim:
1. An exothermic composition comprising by weight, 10-30% of a particulate
readily oxidizable metal; an oxidizing agent for the metal in an amount of
up to 20%; 0.05-10% of an organic fluorine-containing compound selected
from the group consisting of polytetrafluoroethylene,
polyhexafluoropropylene, polychlorofluoroethylene and polyvinylfluoride;
5-80% of a particulate refractory material; 1-55% of a refractory fiber;
and a binder in an amount of up to 25%.
2. An exothermic composition according to claim 1 wherein the readily
oxidisable metal is aluminium, magnesium or silicon.
3. An exothermic composition according to claim 1 wherein the readily
oxidisable metal is an alloy containing a major proportion of aluminium,
magnesium or silicon.
4. An exothermic composition according to claim 1 wherein the oxidising
agent is one or more of iron oxide, manganese dioxide, sodium nitrate,
potassium nitrate, sodium chlorate or potassium chlorate.
5. An exothermic composition according to claim 1 including a binder which
is one or more of phenol-formaldehyde resin, urea-formaldehyde resin, gum
arabic, sulphite lye, starch or colloidal silica derived from colloidal
silica sol.
6. An exothermic composition according to claim 1 wherein the particulate
refractory material is silica sand, alumina or an aluminosilicate.
7. An exothermic composition according to claim 1 in which at least a
proportion of the particulate refractory material is a lightweight
material of density less than 0.5 g/cm.sup.3.
8. An exothermic composition according to claim 7 wherein the lightweight
particulate refractory material is perlite, diaomite or calcined rice
husks.
9. An exothermic composition according to claim 1 including refractory
fibres which are aluminosilicate fibres or calcium silicate fibres.
10. An exothermic composition according to claim 1 and containing organic
fibres.
11. An exothermic composition according to claim 10 wherein the organic
fibres are paper.
12. An exothermic composition according to claim 10 wherein the quantity of
organic fibres present is up to 8% by weight of the composition.
13. An exothermic composition according to claim 1 containing 0.1-6% by
weight organic fluorine-containing compound.
14. A preformed shape for lining parts of molds used in the casting of
molten metals and formed of an exothermic composition according to claim
1.
Description
This invention relates to exothermic compositions, and particularly to
exothermic compositions used in the casting of molten metals.
When molten metal is cast into a mould and allowed to solidify the metal
shrinks during solidification and its volume is reduced. In order to
compensate for this shrinkage and to ensure that sound castings are
produced it is usually necessary to employ so-called feeders located above
and/or at the side of castings. When the casting solidifies and shrinks
molten metal is fed from the feeder(s) into the casting and prevents the
formation of shrinkage cavities. In order to improve the feeding effect
and to enable the feeder volume to be reduced to a minimum it is common
practice to surround the feeder cavity and hence the feeder itself with an
exothermic or exothermic and heat-insulating composition which retains the
feeder metal in the molten state for as long as possible.
For the same reason it is also common practice in the casting of ingots,
for example steel ingots, to line the head of an ingot mould or a head box
fitted to an ingot mould with an exothermic composition or an exothermic
and heat-insulating composition.
In both applications the exothermic or exothermic and heat-insulating
compositions are commonly used in the form of preformed shapes such as
cylindrical sleeves for lining the feeders of foundry casting moulds and
boards for the lining of ingot mould heads or head boxes.
Exothermic or exothermic and heat-insulating compositions are also used,
either as preformed boards, or in particulate form, for example as powders
or granules (known as anti-piping compounds), to cover the surface of
molten metal in a casting mould feeder or in an ingot mould or the head
box of an ingot mould.
The exothermic compositions employed in the applications described above
usually consist essentially of a metal which is readily capable of
oxidation, usually aluminium, and an oxidising agent therefore, for
example iron oxide, sodium nitrate or manganese dioxide. The composition
will usually contain a particulate refractory filler, and when used as a
preformed shape, a binder. Preformed shapes which are to be
heat-insulating as well as exothermic will usually contain a fibrous
material and/or a light-weight particulate refractory material.
In order to improve the sensitivity of the exothermic composition, i.e.
reduce the time lag between applying to the composition a temperature at
which it will ignite and the actual ignition of the composition, it was
proposed some years ago to include in the composition a proportion of an
inorganic fluoride salt. Examples of inorganic fluoride salts which may be
used for this purpose include simple fluorides such as sodium fluoride,
potassium fluoride, lithium fluoride or magnesium fluoride, and complex
fluorides such as sodium silicofluoride, potassium silicofluoride, sodium
aluminium fluoride or potassium aluminium fluoride. Exothermic
compositions containing inorganic fluoride salts are described in British
Patents 627678, 774491, 889484 and 939541.
Although it has become universally accepted that a fluoride salt must be
present, from environmental considerations the presence of fluoride salts
in exothermic compositions is undesirable. It is therefore preferred that
the fluorine content of the compositions is held at as low a level as
possible commensurate with a satisfactory sensitivity.
It has now been found that an organic fluorine-containing compound can be
used advantageously at reduced levels compared with an inorganic fluoride
salt in such exothermic compositions.
According therefore to the present invention there is provided an
exothermic composition comprising a particulate readily oxidisable metal
and an organic fluorine-containing compound.
The readily oxidisable metal may be for example aluminium, magnesium or
silicon, or an alloy containing a major proportion of one or more of these
metals. Aluminium or an aluminium alloy is preferred.
The organic fluorine-containing compound may be a fluorocarbon polymer such
as polytetrafluoroethylene or polyhexafluoropropylene, a polymer
containing fluorine and chlorine such as polychlorofluoroethylene, or
polyvinyl fluoride.
Polytetrafluorothethylene in particulate form is preferred. The
polytetrafluoroethylene may be used for example as particles of the pure
compound or as particles of polytetrafluoroethylene filled with a material
such as fibreglass or carbon.
The quantity of organic fluorine-containing compound used in the
composition will usually be from 0.05% to 10.0% by weight, more usually
from 0.1% to 6.0% by weight.
Although it is possible to produce exothermic compositions which rely on
oxygen in the atmosphere as the source of the oxygen required to react
with the readily oxidisable metal to produce heat the composition will
usually also contain an oxidising agent for the metal.
When used the oxidising agent may be for example iron oxide, manganese
dioxide, sodium nitrate, potassium nitrate, sodium chlorate or potassium
chlorate. Two or more oxidising agents may be used in combination if
desired.
The composition will usually contain one or more other components depending
on whether the composition is to be used as a preformed shape or in
particulate form, and on whether it is desired that the composition should
have heat-insulating as well as exothermic properties.
If the exothermic composition is to be used in the form of a preformed
shape such as a sleeve or board the composition will also contain one or
more binders. Examples of suitable binders include resins such as
phenol-formaldehyde resin or urea-formaldehyde resin, gums such as gum
arabic, sulphite lye, starch or colloidal silica derived from colloidal
silica sol.
Compositions which are to be used in particulate form and compositions
which are to be used as preformed shapes may contain a particulate
refractory material such as silica sand, alumina or an aluminosilicate
such as grog or chamotte.
In order to improve the heat-insulating properties of the composition after
completion of the exothermic reaction at least a proportion of the
particulate refractory material may be a lightweight material of density
less than about 0.5 g/cm.sup.3 such as perlite, diatomite or calcined rice
husks, and/or the composition may contain refractory fibres such as
aluminosilicate fibres or calcium silicate fibres, and/or organic fibres.
The compositions of the invention will usually contain by weight:
______________________________________
readily oxidisable metal
10-30%
oxidising agent 0-20%
organic fluorine- 0.1-6%
containing compound
particulate refractory
5-80%
material
refractory fibre 1-55%
organic fibre 0-8%
binder 0-25%
______________________________________
Weight for weight solid organic fluorine-containing compounds are more
efficient than inorganic fluoride salts in improving the sensitivity of an
exothermic composition.
The following example in which prior art compositions are compared with
compositions according to the invention will serve to illustrate the
invention:
A series of six sleeves was prepared from a basic composition consisting of
aluminium powder and foil particles as oxidisable metal, manganese dioxide
as oxidising agent, particulate alumina, aluminosilicate fibres and paper,
and phenol-formaldehyde resin and colloidal silica sol as binders. Four of
the sleeves contained inorganic fluoride salts and two sleeves contained
polytetrafluoroethylene.
The sensitivity of the exothermic composition of each of the sleeves was
determined by placing the sleeve on a plate heated to 1400.degree. C. and
measuring the time taken for ignition to commence.
The identity and amounts of the flourine-containing compounds used and the
results which were obtained are tabulated below:
______________________________________
FLOURINE-CONTAINING
% BY SENSITIVITY
COMPOUND WEIGHT (SECS)
______________________________________
1 Sodium aluminum fluoride
3.0 30
(min. 93% purity)
Potassium aluminium
1.0
fluoride
2 Sodium silicofluoride
4.0 43
3 Sodium aluminium fluoride
4.0 54
(min. 60% purity)
4 Magnesium fluoride 4.0 53
5 Polytetrafluorethylene
4.0 11
6 Polytetrafluorethylene
1.5 25
______________________________________
Top